This invention relates to cell biology and more specifically to the control of cell proliferation. Proteoglycans are proteins that carry one or more glycosaminoglycan chains. The known proteoglycans carry out a wide variety of functions and are found in a variety of cellular locations. Many proteoglycans are components of extracellular matrix, where they participate in the assembly of cells and effect the attachment of cells to the matrix.
One of the key functions of the extracellular matrix is the storage and presentation of growth factors to cells. Proteoglycans are important mediators of growth factor binding, and they have been shown to modulate the biological activities of a variety of growth factors through interaction via their glycosaminoglycan moieties as well as their core proteins (Ruoslahti, 1989; Ruoslahti and Yamaguchi, 1991).
Growth factors that bind to glycosaminoglycans include acidic and basic FGF (see Burgess and Maciag, 1989), GM-CSP, interleukin-3 (Roberts et al., 1988), pleiotrophin (Li et al., 1990), amphiregulin (Shoyab et al., 1988), HB-EGF (Higashiyama et al., 1991) and platelet factor 4 (Huang et al., 1982), each of which binds avidly to heparin and heparan sulfate. The binding of FGFs to heparin or to heparan sulfate proteoglycans protects the growth factors from proteolytic degradation and is thought to create a matrix-bound growth factor reservoir (Saksela et al., 1988; Gospodarowicz et al., 1990) from which the growth factor can be released in an active form by partial proteolysis of the proteoglycan core protein or through degradation of the heparan sulfate moiety of the proteoglycans (Saksela and Rifkin, 1990; Ishai-Michaeli et al., 1990). Basic FGF has to be bound to glycosaminoglycan to be able to interact with its signal transduction receptor (Yayon et al., 1991; Rapraeger et al., 1991).
The binding of TGF-.beta. to proteoglycans represents a different type of growth factor-proteoglycan interaction. TGF-.beta. has been demonstrated to bind to the core proteins of at least two proteoglycans. One of these proteoglycans is is decorin, a small interstitial extracellular matrix proteoglycan that can interact with TGF-.beta. via its core protein (Yamaguchi et al., 1990). Decorin, also known as PG-II or PG-40, is a small proteoglycan produced by fibroblasts. Its core protein has a molecular weight of about 40,000 daltons. The core has been sequenced (Krusius and Ruoslahti, Proc. Natl. Acad. Sci. USA 83: 7683 (1986); Day et al. Blochem. J. 248: 801 (1987), both of which are incorporated herein by reference) and it is known to carry a single glycosaminoglycan chain of a chondroitin sulfate/dermatan sulfate type (Pearson, et al., J. Biol. Chem. 258: 15101 (1983), which is incorporated herein by reference). The only previously known function for decorin is binding to type I and type II collagen and its effect on the fibril formation by these collagens (Vogel, et al., Biochem. J. 223: 587 (1984); Schmidt et al., J. Cell Biol. 104: 1683, (1987)). Decorin (Krusius and Ruoslahti, 1986) is the prototype of a group of proteoglycans characterized by core proteins of .about.40 kDa that consist mainly of leucine-rich repeats of 20 to 24 amino acids (Patthy, 1987). So far, four members of this group of proteoglycans have been cloned; in addition to decorin, these are biglycan (Fisher et al., 1989), fibromodulin (Oldberg et al., 1989) and lumican (Blochberger et al., 1992). Decorin and biglycan are ubiquitous, although they show a quite divergent localization within tissues, with decorin found more in the extracellular matrix of tissues where it is bound to type I collagen (Vogel et al., 1984; Scott, 1986; Brown and Vogel, 1989) and biglycan localized more closely around cells (Bianco et al., 1990). Fibromodulin has a somewhat more restricted distribution with high concentrations in cartilage, tendon and sclera, while low in skin and mineralized bone (Heinegard et al., 1986). Lumican is found mainly in the cornea (Blochberger et al., 1992). Together, these proteins form a superfamily of proteins (Ruoslahti, Ann. Rev. Cell Biol. 4: 229, (1988); McFarland et al., Science 245: 494 (1989)).
The second type of TGF-.beta.-binding proteoglycan is the type III TGF-.beta. receptor, betaglycan (Segarini and Seyedin et al., 1988; Andres et al., 1989). Betaglycan is a cell membrane proteoglycan (Lopez-Casillas et al., 1991; Wang et al., 1991) that apparently is not involved in the TGF-.beta. signal transduction pathway but may function as a cell-surface TGF-.beta. reservoir presenting TGF-.beta. to its signal transduction receptors.
Transforming growth factor .beta.s (TGF-.beta.) are a family of multi-functional cell regulatory factors produced in various forms by many types of cells (for review see Sporn et al., J. Cell Biol. 105: 1039, (1987)). Five different TGF-.beta.'s are known, but the functions of only two, TGF-.beta.1 and TGF-.beta.2, have been characterized in any detail. TGF-.beta.'s are the subject of U.S. Pat. Nos. 4,863,899; 4,816,561; and 4,742,003 which are incorporated by reference. TGF-.beta.1 and TGF-.beta.2 are publicly available through many commercial sources (e.g. R & D Systems, Inc., Minneapolis, Minn.). In some cells, TGF-.beta. promotes cell proliferation, in others it suppresses proliferation. A marked effect of TGF-.beta. is that it promotes the production of extracellular matrix proteins and their receptors by cells (for review see Keski-Oja et al., J. Cell Biochem 33: 95 (1987); Massague, Cell 49: 437 (1987); Roberts and Sporn in "Peptides Growth Factors and Their Receptors" [Springer-Verlag, Heidelberg] (1989)).
While TGF-.beta. has many essential cell regulatory functions, improper TGF-.beta. activity can be detrimental to an organism. Since the growth of mesenchyme and proliferation of mesenchymal cells is stimulated by TGF-.beta., some tumor cells may use TGF-.beta. as an autocrine growth factor. Therefore, if the growth factor activity of TGF-.beta. could be prevented, tumor growth could be controlled. In other cases the inhibition of cell proliferation by TGF-.beta. may be detrimental, in that it may prevent healing of injured tissues. The stimulation of extracellular matrix production by TGF-.beta. is important in situations such as wound healing. However, in some cases the body takes this response too far and an excessive accumulation of extracellular matrix ensues. An example of excessive accumulation of extracellular matrix is glomerulonephritis, a disease with a detrimental involvement of TGF-.beta..
Thus, there exists a critical need to develop compounds that can modulate the effects of cell regulatory factors such as TGF-.beta.. The present invention satisfies this need and provides related advantages.